MOLECULAR-IDENTIFICATION OF A BACTERIUM ASSOCIATED WITH GALL FORMATION IN THE MARINE RED ALGA PRIONITIS-LANCEOLATA

The polymerase chain reaction (PCR) was used to amplify eubacterial sm all-subunit (16S) ribosomal DNA (rDNA) genes from galls of the marine red alga Prionitis lanceolata Harvey (Gigartinales). These tumors cons ist of hypertrophied algal cells containing large numbers of intercell ular bacteria that remain uncultivable. PCR-amplified 16S rDNAs from s urface-sterilized gall tissue plugs were cloned, sequenced, and analyz ed by alignment to available small-subunit rRNA sequences (University of Illinois Ribosomal Database Project). Variable regions were identif ied and used to construct a fluorescently labeled, species-specific ol igodeoxynucleotide probe for whole cell in situ hybridization to the g all symbiont. Probe 949 (PLANC.949) localized the P. lanceolata bacter ial symbiont in preparations from mature gall tissue. This probe did n ot hybridize to the rDNA of closely related bacteria included as contr ols in the same hybridization reactions. In situ hybridization reveale d the presence of the same bacterium in association with P. lanceolata gall formation from three central California localities. Distance and parsimony analyses suggest that this organism is a member of the Prot eobacteria (alpha subdivision; Rhodobacter group) and is most closely related to Roseobacter denitrificans.